1. Field of the Invention
This invention relates to apparatus and method for grinding tapers on elongated stock and more particularly for grinding points on needle stock.
2. Description of the Related Art
The production of quality needles from raw stock involves many different processes and machinery. These varying processes and machinery become more critical in the preparation of surgical needles where the environment of intended use is in humans or animals. Some of the processes involved in the production of surgical grade needles include, inter alia: straightening spooled wire stock; cutting needle blanks from raw stock; providing a bore for receiving suture thread at one end of the blank; tapering or grinding points at the other end of the blank, flat pressing a portion of the needle barrel to facilitate easier grasping by surgical instrumentation; and, where curved needles are desired, curving the needle. During each of these several steps, extreme care must be taken to ensure that only the intended working of the needle is performed and that the other parts of the needle remain undisturbed.
Machines for grinding points of needles are known. Such machines include the Type NS 6, 8, 11 and 15 automatic point grinding machines available from SCHUMAG Machinery, Inc. of Norwood, N.J. Those machines utilize, for example, a transport wheel and saddle arrangement to present wire shafts to a grinding wheel so as to grind points on the ends of the shafts. A notched wheel is provided for spacing apart the wire shafts and presenting them to the grinding wheel surface. Different sized notched wheels are required for different wire shaft diameters. Thus, in order to change diameter shafts being ground, the appropriate notched wheel must first be installed before grinding of the differing diameter shaft needle blanks can take place. This requires shutting down production and fitting the machine with the appropriate notched wheel each time stock having a diameter not appropriate for the current wheel is to be ground.
Additionally, to operate efficiently, these machines require that the minimum wire shaft length must be longer than many of the surgical needles presently in use, thus necessitating additional finishing steps to refine the dimensions of the needles. Therefore, in order to form a finished needle, for example, having a length of 0.875 inches, stock of at least 13/4 inches would have to first be ground and then be clipped to the desired length. By performing the grinding first and then having to clip the needle shaft to the desired length, chances are increased that the needle point will become damaged during handling and clipping. Moreover, clipping the end of needle stock necessitates additional processing and quality control steps. Specifically, any burrs or other irregularities created from the clipping must be removed and samples inspected to ensure the quality of the work.
Machines for grinding point of needles are known to utilize workpiece feed hoppers and workpiece off-load hoppers. Workpiece feed hoppers provide storage means for storing the workpieces and outlet means for discharging the workpieces to a feed point on the point grinding machine. The workpiece off-load hoppers, similarly, have inlet means for receiving workpieces from an off-load point of the point grinding machine and storage means for storing the workpieces. A problem encountered with both the workpiece feed hoppers and with the workpiece off-load hoppers is the jamming of workpieces at the respective feed and off-load points. Jamming typically occurs when two or more workpieces become wedged against each other at the feed and off-load points. In response to the occurrence of jamming, agitating means has been employed to vibrate the workpieces to prevent as well to correct the jamming of workpieces. Although the use of agitating means provides an improved flow of workpieces to and from the point-grinding machine, the geometry of the hoppers remains such that a plurality of workpieces can jam at the feed point and at the off-load point resulting in the shutting down of production to locate the jam and remove the blockage.
With respect to the storage aspect of the workpiece feed and off-load hoppers, known hoppers are mounted to the point grinding machine in a manner which does not facilitate an expedient replacement of hoppers. Typically, workpiece feed hoppers are supplied or filled with a set amount or batch of workpieces to be machined. When the workpiece feed hopper is empty, production ceases until a refilling operation occurs. Similarly, when the workpiece off-load hopper is full, production must be halted until the hopper can be unloaded. The loading and unloading of workpiece feed and off-load hoppers is time consuming and accordingly a significant cost. There is a need to provide workpiece hoppers which minimize the time required to load and unload workpieces from said hoppers.
Down time of known point grinding machines is also encountered when a change in the size of workpieces is desired. The feeding means of the point grinding machine is, like the workpiece hoppers, affixed in a permanent manner to the point grinding machine. The feeder means, not efficiently mounted to facilitate a quick replacement thereof, must be adjusted to properly interface with each size of workpiece to pass therethrough. Adjustment means are typically provided, but again, require production to cease for a significant time while the adjustment takes place. A need therefore exists for providing feeder means which minimize the time required to set up for a different sized workpiece.
Although, as mentioned above, adjustment means are typically provided on known point grinding machines, the adjustment means do not generally provide multiple axis adjustment capability for varying the spacial relationship of the grinding wheel and the transport wheel. As a result, the adjustment means do not adequately compensate for wear of the grinding wheel. A need therefore exists for providing improved adjustment means which provide maximum compensation for wear of the grinding wheel by providing multiple axis adjustment capability. Secondly, as known grinding wheels experience wear which cannot be compensated for by adjustment means, the wheels are redressed in order to maintain the optimum grinding surface configuration. Redressing methods, however, are dangerous and time consuming. Redressing is required because the wheel does not wear equally along the wheel surface, and therefore the areas of greater wear need to be redressed in order to recapture the optimum surface configuration. If the configuration of the wheel were such that the wheel would wear equally along its surface thereby maintaining on optimum surface configuration while experiencing only a reduction in diameter, then adjustment means would be capable of compensating for the wear of the wheel by simply restoring the desired spacial relationship between the grinding wheel and the transport wheel. A need therefore exists for a grinding wheel which has a fixed optimum shape which is configured to wear evenly, minimizing redressing of the wheel, and facilitating wear compensation through adjustment means.
Finally, grinding wheels employed by these known devices typically have a first edge, and a second edge, with respective diameters of the first edge and second edge of substantially equal value. An intermediate portion of the grinding wheel disposed between the first edge and second edge, generally has a smaller diameter than that of the first edge and second edge. Typically, at a point on the intermediate portion equidistant to the first edge and second edge, the diameter of the grinding wheel is less than that at any other point between the first and second edges. As workpieces are exposed to grinding wheel with the above described conventional design, a surface of the workpiece is first put into contact with the grinding wheel at the first edge. As the workpiece is directed towards the midpoint of the grinding wheel, smaller surfaces of the workpiece are exposed to the grinding wheel thereby forming a taper on the workpiece. When the workpiece reaches the midpoint of the grinding wheel, a point has typically been formed on the workpiece. As the workpiece is further directed from the midpoint to the second edge of the grinding wheel, the grinding wheel does not provide grinding on an untreated portion of the workpiece, but is exposed to tapered and point portions of the workpiece. The second half of these known grinding wheels, the second half being the portion of the grinding wheel from the midpoint to the second edge, provides redundant exposure of the grinding wheel to the workpiece. A need therefore exists for a grinding wheel which is capable of grinding tapers and points on elongated stock while minimizing the time and cost associated with redundant exposure of the grinding wheel to the workpiece.
When it is necessary to grind different sized workpieces, or to replace a worn grinding wheel, known grinding machines generally require a significant amount of time to first replace the grinding wheel, and then adjust other components of the grinding machine to accommodate the new wheel. A need therefore exists for a grinding apparatus having grinding wheel which are capable of being replaced with minimum down time and cost associated with the replacement.
When performing the grinding operation using known grinding wheels, known methods attempt to have the same grinding wheel perform all of the grinding on the needle stock, including critical point forming. Typically, it is very difficult to achieve desired point geometry with the same grinding wheel which has an abrasiveness capable of removing large amounts of needle stock material. Accordingly, when using one grinding wheel to perform "roughing" and "polishing," desired needle stock point geometry is often not achieved. A need therefore exists for a method of grinding needle stock tapers and points which achieves desired needle point geometry. The present invention is directed toward apparatus and method for grinding high quality surgical needles while avoiding the disadvantages of known devices.